Method for measuring traps in semiconductors

ABSTRACT

In order to measure the trap concentration in the neighborhood of a P-N junction in a semiconductor body, the junction is subjected to a reverse bias voltage upon which is superimposed a positive-going voltage pulse (reducing the bias voltage) sufficient to saturate the traps. After the pulse has terminated, the transient RF capacitance response of the body is measured at two predetermined times; and an electrical signal representative of the difference in the capacitance is then generated. The profile of this difference in capacitance as a function of temperature of the semiconductor body yields the relative concentration of traps as well as their activation energies in the semiconductor.

Jan. 7, 1975 METHOD FOR MEASURING TRAPS IN SEMICONDUCTORS David Vern Lang, Chatham, NJ.

Bell Telephone Laboratories, Incorporated, Murray Hill, NJ.

Dec. 6, 1973 Inventor:

Assignee:

US. Cl. 324/158 D, 324/60 C Int. Cl G0lr 31/26 Field of Search 324/158 D, 158 R, 158 T, 324/60 C [56] References Cited OTHER PUBLICATIONS Carballes et al., Capacitives Methods. Solid State Communications; Vol. 9; 1971; pg. 1627-1631.

Primary ExaminerAlfred E. Smith Assistant Examiner Ernest F. Karlsen I Attorney, Agent, or Firm-D. l. Caplan [57] ABSTRACT In order to measure the trap concentration in the neighborhoodof a P-N junction in a semiconductor body, the junction is subjected to a reverse bias voltage upon which is superimposed a positive-going voltage pulse (reducing the bias voltage) sufficient to saturate the traps. After the pulse has terminated, the transient RF capacitance response of the body is measured at two predetermined times; and an electrical signal representative of the difference in the capacitance is then generated. The profile of this difference in capacitance as a function of temperature of the semiconductor body yields the relative concentration of traps as well as their activation energies in the semiconductor.

10 Claims, 4 Drawing Figures l4 RF ATTENUAT R VOLTAGE SOURCE AND PHASE GENERATOR SHIFTER JL VAR. k ATT.

($23 l8 l6 fig RFf SE Ii T E R M'XER AMPLIFIER y DOUBLE WIDE BAND X-Y BOX CAR AMPLIFIER AVERAGER Kg PIITENTED JAN 7 5 3.859.595 SHEET 1 BF 2 F/G. l4 3 y f {I2 RF ATTENUATOR VOLTAGE SOURCE AND PHASE GENERATOR \J sHIFTER I] l5 Y '0 H55 VAR [A ATT. I

I6 I PHASE f 8 RF SHIFTER M'XER AMPLIFIER Y DOUBLE WIDE BAND X Y BOX CAR AMPLIFIER 'AVERAGER FIG. 3 i I TEMPERATURE PATENTEUJIN W5 3.859.595 SHEET 2 or 2 FIG. 2

STEP I= HEAT AND MAINTAIN SEMICONDUCTOR SAMPLE AT TEMPERATURE T| STEP 2 APPLY VOLTAGE PULSE ON A REVERSE BIAS VOLTAGE TO SAMPLE STEP 3 MEASURE TRANSIENT RF CAPACITANCE C AT TIME I AFTER PULSE,-WITH BIAS STILL APPLIED TO SAMPLE STEP 4 MEASURE TRANSIENT RF CAPACITANCE C2 AT TIME I2 AFTER PULSE, WITH BIAS STILL APPLIED TO SAMPLE I STEP 5= MEASURE AND RECORD C -C2 STEP 6: HEAT AND MAINTAIN SAMPLE AT TEMPERATURE T2 STEPS 7 TO IO= REPEAT STEPS 2-5 (AT TEMPERATURE T2) cup- 02 FIG. 4 OXYGEN 00 I50 260' 250 360 350 460 450 560 A TEMPERATURE (K) METHOD F R MEASUR N mFIELD. OF THE'INVENTION r "apparatus a J i kmid cte in the case} 0 (1972); capacitance "technique l n V scan's,are described formeasuring'.traplevels in s e m pairs,'in' galliuni"Ph'osphide jlt would therefore .be 'de s r method which can detect suchtr apsas zinc-'oityg'enfin a galliumphpsphide sampl'e. ,.a's wellas other trap's fsuch.

.o fl p c ii t ch q idwi b e pe'r ature-fscan'. More 'over itwould be desirablettdhave 'emi dt td -usi Jah si st t i, whichfi's morefsensitiveto1-lbvvconeentration of M ln accordanceiwith theinvention, 3 Q 'Q the reverse biasvoltage is superimposed up o'n the re e r ww r rs This invention relates to the held of semiconductor bodies. I. y 7 "BAjtjkGaou'no OF'ITHIE INVENTION; I

filtf isknown ing'the ar'tthat. certain impurities a semiconductor g ivefi rise to'localized energy levels in a semi-;

' U conductor ,crystalJv/hich-fcan trap either electrons or ho lelsfThese lo lizedyenergydevels lie'relatively deep in the forbiddenenergybandgapof the semiconductor (crystal ascomparedvvith the, relatively shallow levels-1 j rspo nsible fortheldonor oracceptor levels in the crys' -Q i H tal due toothe'r-t ypes jof-impurities. Therefare basically J ftwo types of'trap'levels afsemiconductor of give n conductivity.-typelfthose le'vels fwhich ten'd'to trap ma jority'carriers and those-which tendfto-trap minority c'arlriers.

in P-type-g'allium phosphideilt is this zinc-oxygen pair:

type oftrap whichis responsible for red'tluminescence .p nr-d ymme a t-emit in diode ji-bfg lium phosphidej ln' thef fabricationi fofi'welh'cofn't'rolled I 1 and reproducibleelectroluminescent diodes'of gallium jphosp'hide it is advantageous in' thj eijprocessingjo'f.such

"diodes'tobe able to measur n a qua ta: an ear y Stage of m nufd ur h jc cm f'tra'ti'on 'o'fboth-uthese' traps in the'sernicohductorgfwhile opticalztechniques have; be'e n deviel traps in semiconductors;'such tjechniq dro letecting: nn otdetect:

y nonradiative tra s,1;m. fpaperb C. TLC-sail tail; as-, lflished in Applied-Physics; Letters; Volum 0 J:a ge 19,3

as oxygen in .the gallium phosphide Sam y I av technique fordetecting-aplurality of ta s timky ap. T a jtnif/ENTloN P-N junctiondiode body issubjectdto areversejb ias voltag'eflnitially; an electrical pulsegtending 'to"reduce verse bias. The pulse is advantageously of,.s uffi icient height and width in order to saturate the traps with I charge carriers. Fordetecting'majority carrier traps, i the pulseheight isadvanta geously'not sufficient to pro- .duce forward current'through the junction; whereas for detecting minority carrier traps, the pulse height should jindeedbesufficient to produceforward current. After .d, jmoreparticularly, to methods fortest-y s' 'know n that oxygen impurities in It he galliinn p'l osphide give rise to. traps-forminority carfiers telectrons) ih,P-type gallium' 1 atureiis proportional to'th'e trap concentration in the i neighborhood of the .P N 1 with zinc as-th' e acce'ptlor impurity, it is also known that. t zinc-oxygen pairsals 'o give rise to minoritycarrier traps I ble for that peak; 1

cessatio'nfof the electrical pulse andas the traps return to thermaliequilibrium, the transient RF (highfrequency.) capacitance of the body is measured and averagedduring two different suitably selected time intervals centered attimes t and after each pulse, typically by'ac. capacitance bridge techniques. Advantageou'sly,;. the lmeasurements of the transient are performed in the ab'sence of illumination on the semiconductor body; By high frequency capacitance ismeant in' the range of-about 0ll 'Megahertg'to about 100 Meg'ahertz. The profilezof the differences-between the "two averagetransient-RE-capacitances,,C(t{-) C(tas a function of temperature ofthe.diode;yields undesirable information.concerning trapsin the neighborhoodjof the P-N-junctiontS'u'ch-af profile contains peaks (.l'ocalmaximayat varioustemperaturesdepending on flthe-trapstiMor'e' specifically,.the heightofapeak in-the difference profile-,' C(t,) -C(t at a particular temperjunctionof the trap responsi- In a specific embodimentoftheljnventio-n. a'g'a llium ".phosphi de diode' itobetested'contains a P-N junction.

The P-typelside of:t he'junctilonjis doped-with zinc and OX-ygen impurities; Whilflthe' N-ftype side .isdoped only" vvith' 'tel luriumjdonor'): impurities The zinc impurities fonthe-P sideiof'theiljunct'ion a e responsible for making "the gallium ph'osphide P-typesL -whereas the oxygen im purities produce; both oxygen traplevels' aswell as zinc oxygenpair type oft'rap levispnfthis P's'idefof the junc jtionl The differences in the t'ransi efntI-RE'capacitances, C(t C(t atjthei two-predetermined intervals of' time .are-jmeasuredsubsequent to the' applicationtothe. I junctiontof a-forward goi'ng;volt-age-pulse,"wh ich is su-.

perimposed-upon a reverse hias electricaldl'c voltage.

The; profile 0f C( ti) C( 1 asa functionaoftemperature"yiel dsjfthe desiredinformation .as to the presence a'rid relative concentrations of both 'o'x yge n traps and zinc-oxygen ipair type traps in the 'galliumphosphide P-.type rteg' ion in th'e' neighb orlioo'dof the-junction. Ad- A f" fvant'ageouslygithe temperature Tfat vvhichfth ese meas- 'urem'ents of capaczitance. .are performed rangelsufficient'ly' during a single temperature scan'.so as to em-I able. toi have a simplejl.- fbr ackall the trapsfof interest. Specifically, memen o"; detect andjmeasure the presence of both. "oxygen traps andfz'inc-oiiygen' traps, as well. as other trapsof asfyet f.

funknownio'riginjgthetemperatures during'ascan range Baha' j'ijesc mP loNoPIda/twine Q a semiconductor sample in a'cc'o'rdan'ce with the"inven-' "tion,-,

,flFlG'. 2 's'a flow chart of the sequence of steps for test; ihgasemiconductorasample'in'accordance.w'iththein- V nyentiomtogether with its'featuresfadvantages ndlobjec tjs', "may be better understood from-the follow-. detailedidescriptiohwhen read'i'ncohjunction with theidrawing infa which '1 p L 1 is as s'chema'ti'c diagram of-electricalcircuit apparatusnfor'carr ying outa sequence of stepsfo'rf-testing FIG. 3 is a graph useful in explaining the theory of operation of this invention; and

FIG. 4 shows a temperature profile of differential transient RF capacitance response of a P-N junction of gallium phosphide, useful for measuring traps, obtained in accordance with a specific embodiment of the invention.

DETAILED DESCRIPTION As indicated in FIG. 1, a semiconductor diode sample containing a P-N junction to be tested is heated and maintained at a predetermined temperature by means of an auxiliary heating circuit 11. The diode is subjected to a reverse voltage bias, upon which are superimposed voltage pulses, both voltages supplied by the voltage generator 12. The pulse height and width are sufficient to saturate the traps with charge carriers. The diode is placed in parallel electrical relationship with a phase shifting and attenuation network 13 which is adjusted so that minimum RF current flows through the combination of the diode 10 and the network 13 under the influence of an output current from an RF source 14. Thereby, the thermal equilibrium RF capacitance of the sample 10 is offset, and only the RF capacitance transient is detected. A variable RF attenuator 15 is adjusted for optimum signal to noise consistent with reasonably small excursions of the depletion layer width in the diode 10 during RF testing. An RF phase shifter 16 is adjusted so that the capacitive response of the system is maximized. The RF current response of the diode 10 is fed through a bypass capacitor 17 (for d.c. isolation) to an RF amplifier 18. An RF mixer 19 demodulates the thus amplified RF current response to feed only the capacitive component thereof to an amplifier 20. The output of the amplifier 20 is then an amplified signal representative of the instantaneous RF capacitance C of the diode 10. This signal is fed to a double boxcar averager 21 which integrates the signal C over first and second disjoint time intervals centered at t and thereby yielding the two time-averaged RF capacitance signals C(t,) and C(t respectively. The difference signal C(t,) C(1 is then measured at different temperatures of the diode as controlled by the heating circuit 11.

It is helpful to think of the RF capacitances C(t and C(t as the instantaneous (rather than averaged) values of the RF capacitance of the diode at moments of time centered at t, and or, speaking more briefly, the RF capacitances at times t and respectively. But it should be understood that the actual duration of the time intervals centered at t, and can be of arbitrary length so long as these intervals do not overlap.

The foregoing steps performed by the apparatus shown in FIG. 1 are indicated in FIG. 2. The difference signal C(r,) C(t between the respective transient RF capacitances C(t and C(2 is applied to the Y coordinate of an XY recorder 22. The X coordinate of the recorder 22 is controlled by the temperature of the sample semiconductor diode l0 monitored by a thermocouple thermometer 23. Thus, the XY recorder 22 plots the relationship between C(t C(1 versus temperature. Due to the confinement of the depletion region to the neighborhood of the P-Njunction, this capacitance C is attributable almost exclusively to this neighborhood, rather than to the bulk material of the diode.

It should be understood that the temperature of the diode 10 can conveniently be continuously (rather than discretely) varied in time, so long as no significant variation in temperature of the sample occurs during the measurements of C(t and C(t,) for any time period commensurate with the slowest time constant in the system. Thus, the temperature is held substantially constant for each measurement of C(2 C(I As indicated on the left-hand side of FIG. 3, immediately after a pulse is provided by the generator 12, the capacitance decays due to the asymptotic return of the filled and empty trap levels to thermal equilibrium. The rate of decay of the RF capacitance transient is a function of temperature, as indicated on the left-hand side of FIG. 3; so that the differences C(r C(1 for fixed t and t vary with temperature, as plotted as curve 31 on the right-hand side of FIG. 3. Curve 31 is obtained with the same time intervals centered at the same times and after each pulse.

It should be noted in FIG. 3 that the repetition time is denoted by t,;, that is the time between successive voltage pulses (which are indicated as vertical line segments at [=0 and Z At lower temperatures. the capacitance transient does not have sufficient time to decay to thermal equilibrium; consequently, the jumps in capacitance, produced at the moments of the voltage pulses, are of smaller magnitude at lower temperatures.

It should be emphasized that the temperatures, at which the maxima occur in curve 31, depend upon the selection of times t, and t (i.e., the center of the intervals t and for finite intervals). For a given ratio of (I /t however, the sharpness of these maxima remains relatively similar, but the temperatures at which these maxima occur depend upon the values of (1 1 Specifically, for lower values of (t t the maxima occur at higher temperatures. The lower limit on t, in any event is the time it takes for the electronics of the system, particularly in the amplifiers l8 and 20, to recover from the voltage pulses of the generator 12. Typically, this lower limit is about 10 microseconds. The upper limit on t, is of the order of one-tenth the repetition time, t otherwise the signal C(r,) C(r is always relatively small. The time 1 can vary typically between about twice I, to slightly below the repetition time, t The repetition time 1,, is selected sufficiently low for conveniently small duration of the measurements to be made, but I should be at least slightly larger than t to produce a desired sharpness of maxima (as determined by the ratio, 1 m) and at desired temperatures (as determined by the difference, 1 1,).

One advantage of the technique in this invention is that the noise background corresponds to essentially the repetition rate which can be as high as several kilocycles (t less than 1 millisecond), while the technique described in the above-mentioned paper of Sah et al has a noise background corresponding to much lower repetition rates (less than 10 Hertz) at which amplifiers are significantly burdened with more noise background. Accordingly, the noise improvement of this invention over Sah et al is by a factor of between 2 or l0 or more.

At the sacrifice of the appearance of spurious peaks and spurious steps in the profile, this invention can be practiced with only one value of the transient RF capacitance response C(t and plotting this C(m as a function of temperature, instead of measuring both of C(t and C(t and plotting the difference of C(n) the amp t ['c'apaciltori istcbnneqfedflingorder'to.a.c. couple-the am- 'plifie'rIZt) toi thelaveragerjg lj th'ereby. to produce these f'peaks..; ,A'dvantageously; thiswcapacitor is thussufficiently large' su ch that the product of its capacitance and the 'ohmi'c resistanee ofsthefdo ubleiboxcar averager 21' is atgleas't an orde'r offrn agr' itude larger than repetif tion time t ilnithisway thetransient RF capacitance C(tfi will not be'gdistorted i-by relativelyslow spurious i voltagefc'hanges inthe-{biasvoltage appliediacro ss the sample 10 orsuchspuriouschanges generated else.

[wherein the measurement apparatus itself. Moreover,-

" in selecting-the single time interval centered-at ti'jfo r the single'measuiement otqt the limits' onfi thehvah fie .20. nd the double boxcar a'verager 21', a

when using only.

functionlof temperatureLP-I'n thus practicing this invention witho'nly' orie-val tleofcfl peaks in the g temperature prof le?arefstill-observed corresponding to the trapsfprovideda capacitor is connected-between mixer, and the wideband amplifier 20 was a PAR 113. The double boxcar averager 21 was a PAR 164/162 double boxcar averager set to integrate over the two disjoint time intervals t and t each interval having a about 125K toab'out. 500K, thereby, producing an XY I theamplifier 20 and"thelavei ager'21 F 33,be omitted,

in which case the-shape of 'the resulting profile of C(t I i nilartojthat as obtainedi in the technique .o'fjvSa et.alf,f but intermediate I te'd with th'is invention.

asafunction of .tempe'ratu trapsaszinc-oxide can be detmuta e I In atypical example,' by w'ay'of illustration only th' e sample 10 was. a gallium"phosphidexdiod whicli hadj v been grown by doubleliquid 'phaseepitaxy testes; atelluri'um dopedc liquid encapsulated:pzocliralski J (LECYgrown crystal substrate. Thesubs'trat'e had a f-rel. atively high net significant donor-concentration ofJthe order'of-l O 'per cubic centimeter; Upon this substrate thetellurium doped' N typejliPE layer'of 'gallium phos .phide was grown iwithan excess-donorjimpurity con s centration of about 7 1Q- per cubic centimeter. Upon this N-type layer, a P-type 'lay ee-ofgallium phospihide was grown, doped with both zine and-oxygen impurities. to the extent of .about4 l'()"'per cubic centimeterfor" zinc impuritiesand-about2 f1 O1 per cubic ,centim'ete' for oxygen-impurities, thereby forming' 'aP Njunction.. These P and' 'N layefrs were both?" grown at seam 1,'O45? C, then annealedat about 600?? forflaboutafifhours, andat aboutjf 0OCfor=about 9*hours;

The generatorlz'was a Systron Donner-l 10B pulse i"; generator which-furnished-areverse voltage bias to the posed thereon. The riseandffall times of the" pulses diode 10 as wellfas controlledfvolt'agejpulses superir'n were ofthe order of 10 nanoseconds, with pul sei widths iinade withoutdeparting-{minithescopeofthe invenj 'tion. For exampl,e,"-thesemiconductor sample can-"be serniconductive galliuinifia'rsenide,wjthmo'dificationof v fthvoittge pulse supp led'bytliefgenerator12' tiia about jjvoitsj; with a pulse width of ja'bofu t 'l' fniicroseco'nd, n Y

order tojdetect-trapsof asye-tu'nknownorigin with acti- ..V tio n,energies. 'dfp0b76eVjan'd flii ievi respectively'.'; 'Thelampieban also be semicondu ctivlerfsilicon, with i p lse heights of about 10 vo1rs,.wim;la'puis "widr otfl,

-as zgold,fiooba'It;v zinc; silver, boron, and sulfur; "ln. gen era];rdifferentpulse heights and widths arjebest ford" :tectingldifferentnap I 1. It should be understood thatthe instantane'ous'RE-c 'pacitances C(t andflC-(i i can be measured bylot'her'. techniques and electricalisjignalsrepreseritative of C(t C( t itcan be developedjther'ebyffor use in this inv'ennonmtgo; in addition tofP N junctions, Schottkyor other lelectrical "barriers iii-semiconductors cairbe tested for traps -by=using thest'ep nally insteadj of measuringth'ej:

duration of the order of 0.5 milliseconds.

In operation in accordance with this Example, the

' generator 12'was set to provide a reverse bias voltage of about 6 volts, together with pulses, of heights about 10 volts -(to yield 4 volts forward bias) and widths of aboutSO microseconds, superimposed on the reverse 'voltage bias at predetermined intervals. The polarity of the pulse is advantageously in the senseiof decreasing voltage bias; The double boxcar averager 21 was set to detect the capacitance signal output of the amplifier 20; C(t and.C (t respectively at times t and i after "lte'rminatioriof the pulses, with t equal toabout l millise cond'and t about 1O milliseconds. Measurements of .ile's 0 n' ti Yel a e; t esame as-thos'e discussed; en 02 C(11) were recorded in the 1 above for t in the'fcaseof the use of thetwodisjoint.

' time intervals. Evenjusing-on-ly'thesingletime interval? "sCIente'red fat 1 and profiling C( ti) as alfunctigon of term; fi'psr m're; the'technique ofthisfinvention.isi'c'apableiof detecting traps of intermediatedepth in the energy bandgapgt-hatisjless deep thanthose o'bseryablelwithg the aforementioned techniqueof Sah et al.'andof lower concentrafl ifin' than aobservable with said technique 'of 1 sah etaliiMoreover ts'ho'ul d be mentioned that even.

' gle'measurement of "capacitance. T C(t,)1at each temp'e at i e-and scanning the temperature, the aforementioned coupling capa'citor' he'tween.

c'orderl 22 The'temperature'fwas slowly varied from curv' in the recorder, indicated infFlG. 4. There were apparentlythree'peaksflrelative maxima) in the curve. jAs indicated in FIG .:4, one peak corr espo'nded to the Straps"due'itoiZnQ pairsfanother-peak to the oxygen .lpeak 'tdthejoxygentraps and another due to .a trap of "unknown originf Fora given'trap', the height of such p'eaksis proportional to the corresponding concentraof'thattrap "in theneighborlioodiof the l? -N.'junc-v ftion iii. the;semiconductor.'OtherJgalli'um phosphide" sam p'les' havesliowneven more such peaks due'to traps 7 .of unk nown.-or'igi n1, whichfmay be correlatedfwith lumi nous fefficien'cyjof light-emitting ;diodes using these.

samples'jof galliurnqphosphide; I

While this invention has,'beendescr,ibed in terms (if f.

a specific embodiment, va'riousf rnodifications can be lQQQ microseconds; in order to detect-such trap lRF'conduct'an'ce or inductance may also be detected of the order of 20 nanoseconds to "5 milliseconds. TheL-' I RF source 14 was a ZOMHz-RF- oscillator supplying 0:2 volts peak to peak to thediode; and the capacitance of the dc. isolation capacito'i' l7 was 200 picofarads. The

for aipair'o f disjoint? time intervals,centered at t, and

1:1 and'processe'd -in'the same mannerasdescribedtor amplifier 18 was a P AR l 1jit'PrincetonAppliedRee search). The mixer 19; w'as-al le'wl'ett'Packard RF the RF-capacit ance responses.

What is claimed is?- 1. A method orltesti thisin'vention. Fi-I" v nsi eht RF capacifl; i tanc e ,r-ejsponses pf the bojdyito the 'electrical voltage pulses, transieritresponses-such as-electrical current,

I v 7 ng a semiconductor-bodyi'con taining a P N junction which comprisesthesteps 'ofz a. maintaining the P-N junction under a reverse bias voltage at a first temperature through steps (b) through (d);

b. applying a voltage pulse across the P-N junction in the body superimposed on the reversed bias voltage;

c. developing a first signal proportional to the transient RF capacitance of the junctionin the body during a first predetermined time interval after cessation of the pulse;

d. developing a second signal proportional to the transient RF capacitance of the junction in the body during a second predetermined time interval after cessation of the pulse; and

e. developing a third signal proportional to the difference between the first and second signals.

2. The steps recited in claim 1 followed by a repetition of such steps but with the first temperature being changed to a second temperature which is substantially different from the first temperature, all other control parameters being kept substantially the same.

3. The steps recited in claim 2 followed by another repetition of the steps recited in claim 1 with the first temperature being changed to a third temperature which is substantially different from the first and the second temperatures.

4. A method for testing a semiconductor body containing an electrical barrier under a reverse electrical bias which comprises the steps of:

a. maintaining the body substantially at a given temperature during steps (a) through (c);

b. applying an electrical pulse to the body superimposed on the bias;

c. sampling a transient response of the barrier during a first sample time interval after cessation of the pulse and developing an electrical signal representative of the time-averaged transient response of the barrier during the first sample time interval;

d. repeating steps (a) through (c) at a different temperature, all other control parameters being kept substantially the same.

5. A method for testing a body in accordance with claim 4 in which the body is a semiconductor containing a P-N junction under a reverse bias voltage upon which the electrical pulse is superimposed, the transient response being the RF capacitance of the body across the junction.

6. A method for testing a body in accordance with claim Sin which the transient response is the difference between the RF capacitance during two disjoint time intervals after cessation of the pulse.

7. A method for testing a body in accordance with claim 6 in which the semiconductor is gallium phosphide containing zinc and oxygen impurities which produce traps in the gallium phosphide.

8. A method for testing a semiconductor body for traps, the body containing a P-N junction with the traps in the neighborhood of the junction which comprises the steps of:

a. maintaining the neighborhood of the junction substantially at a first temperature during steps (b) through (c) and subjecting the body to a reverse voltage bias during steps (b) through (d);

b. applying a voltage pulse to the body (superimposed on the bias) sufficient to saturate the traps with charge carriers;

0. developing an electrical signal representative of the difference C(t C(t l of the transient RF capacitance of the body during two disjoint predetermined time intervals t and after cessation of the pulse;

d. repeating steps (b) and (0) while maintaining the neighborhood ofthe junction substantially at a second temperature different from the first.

9. The method recited in claim 8 in which the semiconductor is gallium phosphide.

10. The method of claim 8 in which the traps include zinc-oxygen pairs. 

1. A method for testing a semiconductor body containing a P-N junction which comprises the steps of: a. maintaining the P-N junction under a reverse bias voltage at a first temperature through steps (b) through (d); b. applying a voltage pulse across the P-N junction in the body superimposed on the reversed bias voltage; c. developing a first signal proportional to the transient RF capacitance of the junction in the body during a first predetermined time interval after cessation of the pulse; d. developing a second signal proportional to the transient RF capacitance of the junction in the body during a second predetermined time interval after cessation of the pulse; and e. developing a third signal proportional to the difference between the first and second signals.
 2. The steps recited in claim 1 followed by a repetition of suCh steps but with the first temperature being changed to a second temperature which is substantially different from the first temperature, all other control parameters being kept substantially the same.
 3. The steps recited in claim 2 followed by another repetition of the steps recited in claim 1 with the first temperature being changed to a third temperature which is substantially different from the first and the second temperatures.
 4. A method for testing a semiconductor body containing an electrical barrier under a reverse electrical bias which comprises the steps of: a. maintaining the body substantially at a given temperature during steps (a) through (c); b. applying an electrical pulse to the body superimposed on the bias; c. sampling a transient response of the barrier during a first sample time interval after cessation of the pulse and developing an electrical signal representative of the time-averaged transient response of the barrier during the first sample time interval; d. repeating steps (a) through (c) at a different temperature, all other control parameters being kept substantially the same.
 5. A method for testing a body in accordance with claim 4 in which the body is a semiconductor containing a P-N junction under a reverse bias voltage upon which the electrical pulse is superimposed, the transient response being the RF capacitance of the body across the junction.
 6. A method for testing a body in accordance with claim 5 in which the transient response is the difference between the RF capacitance during two disjoint time intervals after cessation of the pulse.
 7. A method for testing a body in accordance with claim 6 in which the semiconductor is gallium phosphide containing zinc and oxygen impurities which produce traps in the gallium phosphide.
 8. A method for testing a semiconductor body for traps, the body containing a P-N junction with the traps in the neighborhood of the junction which comprises the steps of: a. maintaining the neighborhood of the junction substantially at a first temperature during steps (b) through (c) and subjecting the body to a reverse voltage bias during steps (b) through (d); b. applying a voltage pulse to the body (superimposed on the bias) sufficient to saturate the traps with charge carriers; c. developing an electrical signal representative of the difference C(t1) - C(t2) of the transient RF capacitance of the body during two disjoint predetermined time intervals t1 and t2 after cessation of the pulse; d. repeating steps (b) and (c) while maintaining the neighborhood of the junction substantially at a second temperature different from the first.
 9. The method recited in claim 8 in which the semiconductor is gallium phosphide.
 10. The method of claim 8 in which the traps include zinc-oxygen pairs. 